1. Field of the Invention
The present invention relates to a diode element circuit and a switch circuit using the same and, more specifically, relates a diode element circuit formed in an IC form having a high break down voltage and a small leakage current which is suitably used for the switch circuit in an IC tester.
2. Background Art
As typical conventional diodes which are formed in a monolithic IC circuit and perform rectification, a schottky barrier diode which utilizes a schottky junction between a metal and a semiconductor and a PN junction diode which utilizes a PN junction between a P type semiconductor and an N type semiconductor are enumerated. Among those, the schottky barrier diode has an advantage of a high break down voltage and a disadvantage of a large leakage current in a reverse direction.
The PN junction diodes include one using a PN junction between base and emitter of a transistor and one using a PN junction between base and collector of a transistor. A PN junction diode using a PN junction between base and emitter of a transistor which is generally used has an advantage of a small leakage current, but has a disadvantage of a low break down voltage. On the other hand, a PN junction diode using a PN junction between base and collector of a transistor shows a high break down voltage, but has a disadvantage of causing a leakage current to a substrate during being used in forward direction operation because of an influence of parasitic transistors around the junction.
Accordingly, in order to achieve at the same time both a small leakage current and a high break down voltage, a variety of measures have been proposed which devise material and structure of the diodes. As examples thereof, with regard to the schottky barrier diodes, JP-A-9-199733 (1997) is enumerated and with regard to the PN junction diodes JP-A-7-66433 (1995) is enumerated.
However, these measures bring about problems of requiring a special additional manufacturing process and difficulty of using a conventional manufacturing method and manufacturing device as they are. Further, since these measures complicate the manufacturing process, which causes problems of reducing the yield and increasing the manufacturing cost.
An object of the present invention is to resolve the above conventional problems and to provide a diode element circuit which requires no additional manufacturing process and realizes a small leakage current and a high break down voltage.
Another object of the present invention is to provide a switch circuit which achieves at the same time both a small leakage current and a high break down voltage and is, in particular, suitable for use in an IC tester.
A diode element circuit and a switch circuit using the same according to the present invention which achieve the above objects are characterized, in that in a diode element circuit formed in an IC which includes an anode electrode and a cathode electrode and uses a diode of a PN junction between base and collector of a PNP transistor, the PNP transistor is a vertical type transistor formed in a well region, and a voltage drop element which is connected between the collector of the transistor and the anode electrode is included, wherein the base of the transistor is connected to the cathode electrode and the well region is connected to the anode electrode.
As indicated in the above structure, the PN junction between base and collector of the PNP transistor which shows a small leakage current in the reverse direction is used, and in order to reduce a leakage current to a substrate due to parasitic transistors in the PNP transistor the voltage drop element is inserted between the anode electrode and the collector thereof as a bias circuit. Thereby, the collector side is placed in a lower potential than the well region to induce a potential difference therebetween. With this measure, the emitter potential of a PNP parasitic transistor is reduced which is constituted by the collector region of the PNP transistors serving as an emitter and the well region thereof serving as a base.
As a result, since a reverse bias is applied between the base and emitter of the parasitic transistor, when a forward current is flown and even when a current between the base and collector of the PNP transistor increases and a voltage drop is generated in the well region, a current value where the parasitic transistor is turned ON can be increased. Accordingly, if the diode is operated under a condition below such large current value, the leakage current from the collector region to the substrate is reduced to substantially zero.
As a result, the diode element circuit according to the present invention can realize a diode having a small leakage current and a high break down voltage in a monolithic IC circuit without adding a manufacturing process. Thereby, the switch circuit constituted by the diode element circuit likely enjoys the above advantages.